1. Technical Field
The present disclosure relates to methods and apparatuses for in-band full-duplex (IFD) multiple-input multiple-output (MIMO) transmission and reception, and more specifically, to methods and apparatuses for the IFD MIMO transmission and reception which can enhance performance of self-interference cancelation (SIC).
2. Related Art
The in-band full duplex (IFD) is a technique for simultaneously transmitting and receiving signals in the same band. It is a technology that can theoretically increase a link capacity up to twice as much as a usual half-duplex (HD) method. However, in the IFD scheme, there is a problem that a self-transmitted signal is introduced into a receiver, and a strong self-interference (SI) signal is generated. Therefore, the SI should be cancelled in order to achieve smooth communications by the IFD method. Usually, a self-interference cancellation (SIC) technique has a problem in that implementation complexity of a transceiver increases. In particular, when the IFD transmission and reception technology is extended to a multiple-input multiple-output (MIMO) system, there is a problem in that the implementation complexity of the transceiver becomes worse due to application of the SIC.
Particularly, a main reason for the high complexity of the SIC in a digital domain is generation of nonlinear SI from nonlinear elements in the transceiver. Such the nonlinear SI is mainly due to nonlinear distortion of a transmission signal. In the conventional HD communications, the nonlinear distortion is lowered below a noise level due to a pathloss, so that it does not cause a big problem. However, in the case of the IFD transceiver in which the transmission signal is directly introduced as SI, the noise level of the nonlinear distortion of the transmission signal can be introduced with a power of several tens of dB or more higher than that of an effective reception signal. Therefore, the SI due to such the nonlinear distortion also should be cancelled.
Especially, in the case of IFD MIMO transmission and reception, the non-linearity of the SI becomes worse due to crosstalk between antennas generated inside and outside the transceiver. Also, since such the nonlinearity of the SI increases a bandwidth of a SI signal, there is a problem of increasing interference between adjacent channels in the IFD transmission and reception system in which multiple channels are used.